This invention relates generally to a method of accurately determining the characteristics and properties of materials, and more particularly to a method for determining the shear absorption parameter in viscoelastic materials.
In many acoustical applications it is necessary to know the shear absorption of a particular composition or sample of a viscoelastic material, for example, to determine whether the material will be an effective sound absorber. Or, it may be necessary to determine the effect of a change in composition on the absorption effectiveness of the material. However, while this is one of the most important viscoelastic parameters, it is also one of the most difficult to determine.
Conventional methods of determining shear absorption do not involve a measurement of acoustical parameters that can be directly correlated with the shear absorption, rather, the desired parameter is derived by subtracting the effects of various other parameters from the overall acoustic response of the material under consideration. This method is less than accurate and is quite cumbersome. One particular method requires that a shear wave be made to longitudinally propagate along a strip of the material while measurements are made of the amplitude decay of the wave as it travels along the strip. This may require various strip thicknesses, and in general such methods are laborious.